Security cards are widely used for various applications such as identification purposes (ID cards) or financial transfers (credit cards). Such cards typically consist of a laminated structure consisting of various plastic layers wherein one or more layers carry information, e.g. alfanumeric information, logo's, a picture of the card holder, etc. Writable cards wherein the user can store random information are also known, e.g. cards comprising a magnetic strip, optically-recordable cards or cards comprising an electronic chip, sometimes called `smart cards`.
A principal objective of such security cards is that it cannot be easily modified or reproduced in such a way that the modification or reproduction is difficult to distinguish from the original. Therefore, security cards are provided with security features which are difficult to modify or reproduce, e.g. a "security seal" between the information layer and a protective sheet bonded to it. Upon an attempt to separate the protective sheet from the information layer, the security seal is destructed or removed so that it becomes clear that the information carried by the card has been tampered with or altered. Such a security seal can e.g. be provided by applying heat-sealable polymers so as to obtain a sealed envelope-type pouch, as described in e.g. U.S. Pat. No. 4,322,461 and references therein.
A problem associated with information recording materials is their susceptibility to mechanical impact which may cause defects such as scratches and may result in a considerable loss of the recorded data. The recordable layer of most of these security cards comprise a plastic foil as protective layer on top of the recording medium. The life-time of such recording materials, which is required to be 10 years for some applications, is insufficient because the plastic foil is not an efficient barrier against solvents, oxygen, moisture and other potential causes of data loss.
Some disclosures mention the use of glass as a base material for making a security card. JP-A 60/214996 describes a laser recording card wherein the base material, which carries the recording layer(s), can be glass. EP-A 272875 also describes an optical recording card wherein glass can be used as a constituting layer. In these patent applications, the glass layer is used as a suitable substrate because of its high transparency so that a light source can be used for writing and reading information. However, the glass layers disclosed therein are non-flexible layers which can easily be broken by accident, e.g. by slight bending during handling or while keeping the card in a wallet.
EP-A 669 205 describes a glass/plastic laminate for use as safety glass in vehicles, said laminate comprising a glass pane, an intermediate adhesive layer and a plastic pane, wherein the glass has a thickness from 30 to 1000 .mu.m. A functional layer can be applied to the glass which, after lamination, is sandwiched between the glass and the plastic layer and is thereby protected from outside influences. Also U.S. Pat. Nos. 3,471,356 and 4,600,640 disclose thin-glass laminates for use in automotive and architectural applications.